The contractor will study the feasibility of rf processing techniques to utilize the information available in the rf echo signal. In Phase I of this project, we will investigate the feasibility of on-line processing of rf echo signals to identify and classify intra-cranial echo originating structures. In addieion, we will study some of the characteristics of intra-cranial vasculature echoes using the moving target indicator (MTI) technique. During this phase of the program a phased array system will be constructed on a subcontract basis to assist in intra-cranial investigation. In Phase II, the phased array system will be interfaced with a high-speed A/D converter and scratch pad memory for rapid on-line target acquisition and identification. Results obtained in Phase I will be used as a basis for computations of tissue identification in Phase II.